A. Field of Invention
The present invention is related to wireless communication systems, and more particularly, to a method and system of managing channel elements used for overhead channel group functions in a wireless base station.
B. Description of Related Art
In a typical wireless communication system, an area is divided geographically into a number of cell sites, each defined by one or more radiation patterns created by an emission of radio frequency (RF) electromagnetic (EM) waves from a respective base transceiver station (BTS) antenna. Similarly, BTS antennae are configured for the reception of EM waves emanating from mobile devices. Each cell site is typically further divided into two, three, or more sectors, where the sectors provide transmit and receive radio coverage for a selected area within the cell site.
Associated with the BTS is a plurality of channel elements for processing individual signal channels. Specifically, in CDMA communication systems, individual communication channels are separable due to their use of channel-specific concatenated coding sequences. In the forward channel, a unique PN code (commonly referred to as a short PN code offset) is used to distinguish channels in a given sector from those in surrounding sectors and cells. Within each sector, channels are further distinguished by yet another code, termed a Walsh code. In an adjacent sector, the Walsh codes may be reused because channel separation is provided by a different offset of the short PN code for that sector. In the ANSI/TIA/EIA-95-B-99 standard entitled “Mobile Station-Base Station Compatibility Standard for Wideband Spread Spectrum Cellular Systems” (published Feb. 1, 1999), the contents of which are incorporated by reference herein, there are sixty-four available Walsh codes, while in CDMA 2000 series (TIA/EIA IS-2000 Series, Rev. A, published Mar. 1, 2000), one hundred twenty-eight Walsh codes are available. Both of the ANSI/TIA/EIA-95-B-99 and the TIA/EIA IS-2000 Series, Rev. A, standards are incorporated herein by reference, and are available from the Telecommunication Industry Association, 2500 Wilson Boulevard, Suite 300, Arlington, Va. 22201.
On the reverse channel, from the mobile to the BTS, a slightly different code concatenation is used. The Walsh codes are used to identify a data symbol alphabet, the short PN code is used for synchronization purposes, and the long code PN code is used to identify the individual mobile channel.
On both the forward and reverse links within each sector, channels referred to as the Overhead Channel Group (OCG) are used to facilitate the call setup process for each carrier frequency used in that sector. Each carrier frequency in the sector has an associated OCG. The OCG channels on each carrier of the forward link are (i) the paging channel, which is monitored by inactive mobiles in the sector, thereby allowing the base station to query, or page, the mobile, and (ii) the sync channel, which contains a data stream of system identification and parameter information used by mobiles to access the system. On the reverse link the OCG channels are one or more public access channels used by mobiles to transmit registration requests, call setup requests, page responses, and other signaling information. The public access channels are specific, predetermined offsets of the long PN code.
The signal processing on each of the forward and reverse traffic channels and, in particular, the channels of the OCG, is performed in channel elements (CE) of the BTS. Each BTS has a bank of CEs that are available for use, which typically reside on one or more channel cards within the BTS. CEs may perform the convolutional encoding, block interleaving, and application of the Walsh coding, and long and short coding as described above. Alternatively, the short code for the forward channel (which is unique to the sector), may be applied to the accumulated outputs of the CEs for that sector. Each CE is typically implemented as a transceiver having a transmit side and a receive side. Thus, for each carrier in a given sector, two CEs are capable of handling the OCG channels.
In existing systems, channel element cards are pooled across frequency carriers. Typically, three OCGs are provisioned on one channel element card in a given carrier (assuming a three sector site). In this configuration, an additional three redundant/failover OCGs (a total of six redundant CEs) need to be pre-configured statically on another card that does not have OCGs assigned to it yet. These redundant/failover OCGs will then be available to service the sector carriers that are served by the OCGs on the channel element card that goes out of service. Again, the remaining CEs on the channel element card that has the redundant OCGs may be used for traffic channels.
While system reliability is increased by provisioning three redundant OCGs, the static provisioning of six channel elements for redundancy is an inefficient allocation of system resources. These channel elements could be used to service customer traffic if dynamic assignment of OCG is implemented with this creation. Specifically, channel cards are relatively reliable, and failures are uncommon events.
Consequently, an OCG CE allocation and assignment process for fail-over redundancy that overcomes these and other limitations is desirable.